This research aims to develop a computer program (XENO) to predict plausible metabolites of a xenobiotic compound and further to analyze the plausible biological activity of each metabolite. This will provide the biochemist with an interactive (graphic) analysis tool that will help in predicting what metabolites to look for, and in enumerating plausible pathways by which a given metabolite might have been formed. Metabolic transformations will be encoded in the ALCHEM language developed for representing chemical reactions, and methodology developed for computer-assisted organic synthesis planning will be utilized to evaluate the applicability of a metabolic transformation to a given xenobiotic compound. The system will consider sterochemical, steric, and electronic effects, and will be predictive rather than retrieval based.